Conventionally, various methods have been developed for forming a high insulated region on a print circuit board.
One of the conventional technologies for a print circuit board with a high insulated region is disclosed in Japanese Patent Application Laid-open No. Sho 57-141995 (hereinafter referred to as Nakajima Document), in which a periphery of the high insulated region is completely surrounded by a slit that passes through the circuit board from an upper side to a lower side thereof, and the high insulated region is supported by terminals of an electronic component to be connected. Another conventional technology is disclosed in U.S. Pat. No. 5,490,325 (hereinafter referred to as Niemann Document), in which the periphery of the high insulated region is surrounded by a slit that passes through the circuit board from the upper side to the lower side thereof except for stem portions for supporting the region, and through holes are provided to the stem portions.
Further, another conventional technology for the print circuit board with a high insulated region is disclosed in U.S. Pat. No. 6,854,980 (hereinafter referred to as Iwasaki '980 Document) that is assigned to the applicant of the present application, in which a bottom surface and all side surfaces of the high insulated region are surrounded by a guard conductor. Still another conventional technology is disclosed in U.S. Pat. No. 6,558,168 (hereinafter referred to as Iwasaki '168 Document) that is assigned to the applicant of the present application, in which the bottom surface and all the side surfaces of the high insulated region are surrounded by a guard conductor, and a gap or a trench is provided between the side surface and the high insulated region.
However, according to the conventional technologies, it is difficult to provide a print circuit board with a high insulated region on which surface mount devices (SMDs) are mounted at low cost and high density. The reason thereof is described later in detail, but shortly the reason is as follows. If the slit is used, restrictions on high density mounting will occur for securing strength of the circuit board and from a viewpoint of arrangement of components and wires. In addition, it is not appropriate for cost and size to provide to the circuit board the side surface of the guard conductor as described in Iwasaki '980 and '168 Documents that can be used for insulating between adjacent terminals of the SMD.
Therefore, it is required to provide a print circuit board with a high insulated region at low cost and high density that can be used for preventing leakage between adjacent terminals of the SMD, and a method of manufacturing the same.